• 전산구조공학
• /
• 제8권4호
• /
• pp.129-136
• /
• 1995

본 연구에서는 Biot의 선형압밀이론에 근거한 2차원 압밀문제의 근사해를 구하기 위한 경계요소법을 제시한다. 먼저 선형 압밀문제의 기초미분방정식의 시간의존성을 제거하기 위하여 시간에 대한 Laplace변환을 적용시키고, 변환공간에서의 미분방정식을 대상으로 정식화를 한다. 변환공간에서의 변위와 간극수압에 대한 경계적분방정식계를 유도하고, 변환공간에서의 연성문제에 대한 기본해를 구체적으로 보인다. 변환공간에서의 해를 실공간의 해로 변환하기 위하여 Hosono의 수직 Laplace역변환법을 적용하였으며, 해석예로서 2차원 반무한 지반의 국소재하에 의한 압밀문제를 해석예로 선택하였고, 암밀해와 비교하여 제안해법의 적용성 및 타당성을 보였다.

• Structural Engineering and Mechanics
• /
• 제2권1호
• /
• pp.49-62
• /
• 1994

Based on the transfer matrix approach and integral transforms, a solution method is developed for the stress analysis of axisymmetrically loaded transversely isotropic elastic media with generalized interlayer and support conditions. Transfer functions (Green's functions in the transformed domain) are obtained in explicit integral form. For several problems of practical interest with different loading and support conditions, solutions are worked out in detail. For the inversion operation, an efficient technique is introduced to remedy the slow convergence of numerical integrals involving oscillating functions. Several illustrative examples are considered and numerical results are presented.

• 지구물리와물리탐사
• /
• 제16권4호
• /
• pp.211-216
• /
• 2013

일반적으로 평활화 필터는 주변값들과의 차이를 감소시켜 함수를 정규화하는 역할을 한다. 따라서 완전파형역산에 평활화 필터를 적용하면 역산 해를 정규화 할 수 있으며 실제 지하 구조에 가까운 영상을 얻을 수 있다. 다만 단일 평활화 계수를 사용했을 때는 지층 형태나 속도변화에 관계없이 동일하게 평활화가 이루어지므로 지층간 경계면이나 단층 등의 구조가 불명확해지는 단점이 있다. 본 논문에서는 이러한 문제를 해결하기 위해 단일 평활화 계수가 아닌 역산 반복 과정에 따라 선택적으로 평활화 계수를 조정하는 정규화 기법을 개발하였다. 먼저 파형역산에 적합한 탐사자료의 주파수 대역과 그에 대응하는 파수 범위를 분석하였다. 분석한 파수 범위에 적합한 평활화 계수를 선정하기 위해 평활화 필터의 파수 스펙트럼에서 99백분위수에 해당하는 파수를 유효최대파수로 결정하였다. 선정된 평활화 계수를 반복역산에 따라 다르게 적용하여 여러 주파수를 동시에 이용하는 멀티-스케일 완전파형역산을 구현하였다. 암염 모델과 같은 속도대비가 큰 지질구조에 대해 성공적인 역산결과를 얻음으로써 본 연구에서 개발한 평활화 계수 선택기법이 효과적인 정규화 과정을 구현한다는 것을 알 수 있었다. 또한 무작위 잡음이 더해진 인공합성 음원모음 자료에 대한 수치예제를 통해 현장 자료에 대한 적용 가능성도 확인할 수 있었다.

• Journal of Electrical Engineering and Technology
• /
• 제10권1호
• /
• pp.308-313
• /
• 2015

This paper describes a technique for complete identification of a two-dimensional scattering object and multiple objects immersed in air using microwaves where the scatterers are assumed to be a homogenous dielectric medium. The employed technique consists of initially retrieving the shape and position of the scattering object using a linear sampling method and then determining the electric permittivity and conductivity of the scatterer using adjoint sensitivity analysis. Incident waves are assumed to be TM (Transverse Magnetic) plane waves. This inversion algorithm results in high computational speed and efficiency, and it can be generalized for any scatterer structure. Also, this method is robust with respect to noise. The numerical results clearly show that this hybrid approach provides accurate reconstructions of various objects.

• 전기학회논문지
• /
• 제67권2호
• /
• pp.248-254
• /
• 2018

In this paper, a Monte Carlo-based Recursive Least Square(MC-RLS) method is presented to directly identify the inverse model of the dynamical system. Although a RLS method has been used for the identification based on the deterministic data in the closed loop controlled form, it would be better for RLS to identify the model with random data. In addition, the inverse model obtained by inverting the identified forward model may not work properly. Therefore, MC-RLS can be used for the inverse model identification without proceeding a numerical inversion of an identified forward model. The performance of the proposed method is verified through experimental studies on a control moment gyroscope.

• 소음진동
• /
• 제9권2호
• /
• pp.377-386
• /
• 1999

This paper is a study on model method for estimating system inputs from vibration responses, which is one of indirect input identification methods in frequency domain. The method has advantages over direct inverse method especially when points of operational inputs are inaccessible so that artificial excitation forces cannot be applied to obtain frequency response functions of the complete system. Procedures of extended modal model method are proposed and checked by numerical experiment. Mechanisms of error propagation, i.e., how errors in modal parameters such as poles nad mode shape vectors affect estimation of the input forces, are illustrated. Then, in order to counteract the error propagation, discrete modal filter approach is taken in this paper to compute the inversion of modal matrix in which the most serious errors seem to be generated. Further, a Reduced form of Modified Reciprocal Modal Vector(RMRMV) is proposed for estimating multiple inputs. It is shown to have smaller orthogonality error than MRMV.

• Journal of the Korean Physical Society
• /
• 제73권9호
• /
• pp.1269-1278
• /
• 2018

Using the thawed Gaussian wave packets [E. J. Heller, J. Chem. Phys. 62, 1544 (1975)] and the adaptive reinitialization technique employing the frame operator [L. M. Andersson et al., J. Phys. A: Math. Gen. 35, 7787 (2002)], a trajectory-based Gaussian wave packet method is introduced that can be applied to scattering and time-dependent problems. This method does not require either the numerical multidimensional integrals for potential operators or the inversion of nearly-singular matrices representing the overlap of overcomplete Gaussian basis functions. We demonstrate a possibility that the method can be a promising candidate for the time-dependent $Schr{\ddot{o}}dinger$ equation solver by applying to tunneling, high-order harmonic generation, and above-threshold ionization problems in one-dimensional model systems. Although the efficiency of the method is confirmed in one-dimensional systems, it can be easily extended to higher dimensional systems.

• 한국정밀공학회지
• /
• 제12권7호
• /
• pp.99-106
• /
• 1995

Frequency response functions are of great use in dynamic analysis of structural systems. The present paper proposes an efficient method for computation of the frequency rewponse functions of linear structural dynamic models with a sparse, non-proportional damping matrix. An exact condensation procedure is proposed which enables the present method to condense the matrices without resulting in any errors. Also, an iterative scheme is proposed to be able to avoid matrix inversion in computing frequency response matrix. The proposed method is illustrated through a numerical example.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회A
• /
• pp.332-336
• /
• 2007

Temperature is an essential process variable in nanoimprint lithography(NIL) where the temperature varies between room temperature and above the glass transition temperature. To simulate NIL process, we employ both the Nose-Poincare method for temperature controlled molecular dynamics(MD) and force field for polymer material i.e. polymethyl methacrylate(PMMA), which is most widely selected as NIL resist. Nose-Poincare method, which convinces the conservation of Hamiltonian structure and time-reversal symmetry, overcomes the drawbacks inherent in the conventional methods such as Nose thermostat and Nose-Hoover thermostat. Thus, this method exhibits enhanced numerical stability even when the temperature fluctuation is large. To describe PMMA, we adopt the force field which account for bond stretch, bending, torsion, inversion, partial charge, and van der Waals energy.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• 제4권1호
• /
• pp.49-65
• /
• 2000

A method for inverting the Laplace transform is presented, using a finite series of the classical Legendre polynomials. The method recovers a real-valued function f(t) in a finite interval of the positive real axis when f(t) belongs to a certain class ${\mathcal{W}}_{\beta}$ and requires the knowledge of its Laplace transform F(s) only at a finite number of discrete points on the real axis s > 0. The choice of these points will be carefully considered so as to improve the approximation error as well as to minimize the number of steps needed in the evaluations. The method is tested on few examples, with particular emphasis on the estimation of the error bounds involved.